This type of servovalve is used, for example, to control the hydraulic vehicle brakes, in particular the brakes of airplanes.
Pressure-regulator servovalves are known that comprise a body presenting a utilization port, a pressure feed port, and a return port, together with a distributor spool mounted to move in the body in such a manner as to put the utilization port into communication either with the pressure feed port or with the return port. The ends of the spool co-operate with the body to define two pilot chambers connected to nozzles which are arranged facing each other so as to open out into a cavity connected to the return port. A vane extending in the cavity between the nozzles is mounted to be moved in controlled manner. The pilot chambers are connected via constrictions to the pressure feed port.
Causing the vane to change position between the nozzles enables the pressures that exist in the pilot chambers to be modulated, and thus enables the spool to be moved in order to modulate the utilization pressure.
That type of servovalve has the drawback of presenting a high rate of leakage. Hydraulic fluid flows permanently through the nozzles and is returned via the return port.
That leakage makes it necessary to dimension the hydraulic fluid tanks accordingly so as to guarantee that the vehicle can be braked even in the event of a breakdown in hydraulic pressure generation.